Most of the dynamics in natural daylight are rather slow and gradual. For example, the blue sky in the afternoon changes into a warm glow in the evening and into darkness at night. The brightness of sunlight, as well as its color and direction, varies over time. The slow and gradual changes contribute to a rich experience of natural light. In contrast, artificial light is often considered to be dull, due to the static and constant quality of light. Therefore, more and more qualities of electric light sources can now be changed over time electronically. For example, dimming the light output of a source is the most basic of these parameters. Variation in color temperature is an option that is already applied in practice. The Philips ‘Carpe Diem’ system, for example, applies a pre-programmed cycle of variations in brightness and color temperature in order to simulate a natural daylight cycle.
However, within such artificial light installations these light quality changes are either fixed or pre-programmed. It is a disadvantage of the known systems that there is no or only little interaction between people's activities and the provided artificial light. Systems are known wherein artificial light is activated by simple presence detectors (photo cells) that switch lamps either on or off. Such systems, however, do also not provide an intuitive and natural interaction with people's activities.